Launching '/usr/sbin/dkms install -m snapapi26 -v 0.7.16 2>&1'.
Error! Could not locate snapapi26.ko for module snapapi26 in the DKMS tree.
You must run a dkms build for kernel 2.6.18-4-686 (i686) first.
Error! Your kernel source for kernel 2.6.18-4-686 cannot be found at
/lib/modules/2.6.18-4-686/build or /lib/modules/2.6.18-4-686/source.
You can use the --kernelsourcedir option to tell DKMS where it's located.
exited with status 1.
AcronisÂ TrueÂ ImageÂ Server Setup failed to build kernel modules. Consult /var/log/trueimage-setup.log and /var/lib/dkms/snapapi26/0.7.16/build$

Please note that you should have the sources of your kernel or at least kernel headers installed to let Acronis True Image Agent for Linux compile the necessary modules or to be able to do this manually. Please refer to this article for more information.